1. Field of the Invention
This invention relates to a wireless communication apparatus of a portable telephone set, a portable television receiving set or the like having an antenna element.
2. Description of the Related Art
Various wireless communication apparatus are equipped with an antenna device for radiating or absorbing an electric wave of a predetermined frequency band. For instance, in the current trend of phenomenally spreading portable telephone sets, they are taking a role of information terminal apparatus for transmitting/receiving e-mail letters and various images and exchanging information of different types rather than a role of simple gears for talking with others. Additionally, as broadcasting stations in Japan have started terrestrial digital transmission services, portable telephone sets are expected to take a new role of operating as television receiving sets in the near future.
In view of the above-identified circumstances, many portable telephone sets are currently equipped with a large liquid crystal display for the convenience of users and designed to appeal buyers particularly in terms of portability and uniqueness. In the field of portable telephone sets, so-called stick type telephone sets are giving way to foldable type telephone sets (denoted by 100) as shown in FIG. 1 and bendable type telephone sets (denoted by 110) as shown in FIG. 2.
Referring to FIG. 1, a foldable telephone set 100 includes two cabinets including a first cabinet 101 where an operation panel including ten keys and function buttons is arranged and a second cabinet 102 where a large liquid crystal display 103 is arranged. The first cabinet 101 and the second cabinet 102 are linked to each other by means of a hinge mechanism 104 so as be foldable relative to each other. When the user of a foldable telephone set 100 talks to some other person over the telephone, he or she unfolds the second cabinet 102 from the first cabinet 101 by way of the hinge mechanism 104 as shown in FIG. 1.
Referring to FIG. 2, a bendable portable telephone set 110 includes a first cabinet 111 and a second cabinet 112 that are linked to each other by way of a universal joint mechanism 113 so that they can be moved in three-dimensional directions relative to each other. With a bendable portable telephone set 110, it is possible for the user to turn the second cabinet 112 upside down relative to the first cabinet 111 so as to expose the liquid crystal display 114 to the surface side and bend the second cabinet 112 orthogonally relative to the first cabinet 111 by means of the universal joint mechanism 113. In this state, the operation panel on the first cabinet 111 and the liquid crystal display 114 on the second cabinet 112 face the same direction and the liquid crystal display 114 is arranged horizontally oblong so that the user can conveniently view a television program or some other video image.
Generally, various portable wireless communication apparatus 120 including portable telephone sets includes a cabinet 121 that includes a first cabinet 122 and a second cabinet 123 and the first cabinet 122 is equipped with an antenna element 124 as shown in FIGS. 3 and 4. As the cabinet 121 of the portable telephone set 120 is made to operate as ground line of the antenna apparatus, a high frequency electric current flows through the cabinet 121 as indicated by dotted lines in FIGS. 3 and 4.
In the portable telephone set 120, the input impedance of the antenna element 124 is set to a level that holds the antenna characteristics including the input characteristics and the gain of the antenna in the most efficient conditions by an impedance matching circuit. However, portable telephone sets 120 are accompanied by a problem that the optimized input impedance can be shifted to degrade the antenna characteristics as the cabinet 121 is held by hand by the user and the head of the user comes very close to the antenna element 124 when the user talks over the telephone. Techniques for coping with the problem are disclosed in Patent Document 1 (Jpn. Pat. Appln. Laid-Open Publication No. 2004-166191) and Patent Document 2 (Jpn. Pat. Appln. Laid-Open Publication No. 2004-208219).
Patent Document 3 (Jpn. Pat. Appln. Laid-Open Publication No. 2000-278024) discloses an antenna apparatus that can secure a predefined gain in the receiving frequency band when an object approaches the inverted F-type antenna element from around. The disclosed antenna apparatus includes an inverted F-type antenna element having a plurality of short-circuiting sections that correspond respectively to a plurality of different resonance frequencies and are arranged on a radiative conductor plate having a feed section, a detection means for detecting a state where the resonance frequency fall and a switching means for selecting a short-circuiting section from the plurality of short-circuiting section. When a human body or some other object approaches to make the resonance frequency fall in the antenna apparatus, a switching signal is output from the detection means to the switching means to select an appropriate short-circuiting section in order to prevent the gain from falling by raising the resonance frequency.